Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$25.49	12.311%	$28.6281	$28.63	$28.65	$28.60
Purchase #2	$74.48	12.505%	$83.7937	$83.79	$83.80	$83.80
Purchase #3	$43.27	8.286%	$46.8554	$46.86	$46.85	$46.90
Purchase #4	$53.86	10.224%	$59.3666	$59.37	$59.35	$59.40
Purchase #5	$132.57	9.376%	$144.9998	$145.00	$145.00	$145.00
Purchase #6	$40.69	11.194%	$45.2448	$45.24	$45.25	$45.20
Purchase #7	$43.63	6.220%	$46.3438	$46.34	$46.35	$46.30
7 purchase totals =	$413.99		$455.2322	$455.23	$455.25	$455.20